1. Field of the Invention
This invention relates to an air conditioning unit for automobiles, more specifically, a bypass means for the ambient air introduced into the air conditioning unit to bypass the evaporator therein.
2. Description of the Prior Art
A conventional air conditioning unit for automobiles of the type disclosed, for example, in Japanese Patent Published Application No. SHO-57-172815 comprises a casing for defining a ventilation duct, a fan for drawing the ambient air into the ventilation duct, an evaporator for dehumidifying the introduced ambient air, a heater core for heating the introduced ambient air, and a water collecting portion formed on the bottom wall of the casing near the evaporator so as to receive the water produced at and dripping from the evaporator. The water collecting portion is provided with a drain means to exhaust the collected water out of the air conditioning unit.
Since the evaporator in the conventional air conditioning unit is disposed transversely across the ventilation duct, the ambient air introduced is subject to the flow resistance of the evaporator, thereby decreasing the ventilation efficiency. This is particularly true when it is intended to draw the ambient air into the passenger compartment through ram pressure during running while the air conditioning is halted , or when the fan is operated in order to positively draw the ambient air into the passenger compartment for strong ventilation while the air conditioning is halted.
In addition, when the air conditioning unit is turned on after parking in the hot sunshine, the air emanating from the unit is inclined to smell, which is caused by the warmed evaporator. It takes a relatively long time to cool the warmed evaporator with the ambient air drawn into the conventional air conditioning unit because the ambient air is subject to the flow resistance of the evaporator as set forth previously.